I think there should be another way to unlock worlds. It is actually very simple. Every time you reach a certain level like i think (as an example) you should unlock marleybone at level 30 and like unlock mushu at level 35 and dragonspyre at level 40 cause i think a lot of us dont want to do EVERY quest in krokotopia to unlock marleybone then so on and so on. :-) :-) :-D
You don't have to do every single quest in the world to unlock the next world. You only have to do the storyline quests . The side quests are there for fun and for leveling up